Including feedback information regarding an individual subband of a wireless channel

ABSTRACT

To report feedback information regarding a wireless channel, a mobile station determines whether a predefined condition is satisfied. In response to determining that the predefined condition is satisfied, feedback information regarding an individual one of plural subbands of the wireless channel is included in a first report to be sent to a base station. In response to determining that the predefined condition is not satisfied, aggregate feedback information regarding the plural subbands is included in a second report to be sent to the base station.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/993,330, entitled “Including Feedback Information Regarding anIndividual Subband of a Wireless Channel,” filed Nov. 18, 2010, which isa National Phase Application under 35 USC 371 of PCT/US09/48629, filedJun. 25, 2009, which claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/075,667, filed Jun. 25, 2008 and U.S.Provisional Patent Application Ser. No. 61/077,276, filed Jul. 1, 2008,which are herein incorporated by reference in their entirety as thoughfully and completely set forth herein.

BACKGROUND

Various wireless access technologies have been proposed or implementedto enable mobile stations to perform communications with other mobilestations or with wired terminals coupled to wired networks. Examples ofwireless access technologies include GSM (Global System for Mobilecommunications) and UMTS (Universal Mobile Telecommunications System)technologies, defined by the Third Generation Partnership Project(3GPP); and CDMA 2000 (Code Division Multiple Access 2000) technologies,defined by 3GPP2.

As part of the continuing evolution of wireless access technologies toimprove spectral efficiency, to improve services, to lower costs, and soforth, new standards have been proposed. One such new standard is theLong Term Evolution (LTE) standard from 3GPP, which seeks to enhance theUMTS wireless network.

In some cases, it may be desirable to provide feedback informationregarding a wireless channel, where the feedback information can be sentfrom a mobile station to a base station. The feedback information caninclude information to allow the base station to apply a selectedmodulation and coding to data sent from the base station to the mobilestation. In addition, the feedback information can include an indicationof a quality of a wireless channel.

According to a conventional LTE standard, a wireless channel forcommunicating data is divided into subbands (also referred to as bands).A subset of subbands can be identified as optimal subbands that can beused for communication of data between the base station and the mobilestation. The conventional LTE standard supports multiple modes ofinformation feedback, but they may not be optimal. For example, PUSCH(physical uplink shared channel) reporting Mode 2-2 as defined by theLTE standard does not allow for feedback information regarding thewireless channel to be provided on an individual subband basis for theselected subbands, which can reduce flexibility and reduce the qualityof data communications over the wireless channel.

SUMMARY

In general, according to a preferred embodiment, to report feedbackinformation regarding a wireless channel, a mobile station determineswhether a predefined condition is satisfied. If so, feedback informationregarding an individual one of plural subbands of the wireless channelis included in a report to be sent to a base station. However, inresponse to determining that the predefined condition is not satisfied,aggregate feedback information regarding the plural subbands is includedin another report to be sent to the base station.

Other or alternative features will become apparent from the followingdescription, from the drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an exemplary arrangement that includes awireless communications network that incorporates a preferred embodimentof the invention;

FIGS. 2 and 3 illustrate different reports that can be communicated froma mobile station to a base station to provide feedback informationregarding a wireless channel, according to a preferred embodiment; and

FIGS. 4-8 are flow diagrams of processes of communicating and/or usingfeedback information regarding a wireless channel, according topreferred embodiments.

DETAILED DESCRIPTION

In the following description, numerous details are set forth to providean understanding of some embodiments. However, it will be understood bythose skilled in the art that some embodiments may be practiced withoutthese details and that numerous variations or modifications from thedescribed embodiments may be possible.

In accordance with some preferred embodiments, a technique or mechanismfor reporting feedback information regarding a wireless channel isprovided, in which feedback information regarding individual subbandscan be provided to a base station. As used here, the term “wirelesschannel” refers to a collection of resources that can be used bywireless nodes, including mobile stations and base stations, tocommunicate wirelessly with each other. The resources includesubcarriers of different frequencies. In addition, resources can includedifferent time slots or different precoding vectors. In one embodiment,a wireless channel can be implemented according to an orthogonalfrequency division multiplexing (OFDM) arrangement in which resources ofthe wireless channel are defined by combinations of time slots (along atime dimension) and subcarriers of different frequencies (along afrequency dimension).

In the OFDM arrangement, a subband (also referred to as “band”) caninclude a number of subcarriers along the frequency dimension and allthe OFDM symbols (time slots) along the time dimension. A wirelesschannel can thus be divided into multiple subbands. More generally, a“subband” refers to some predefined portion of a wireless channel, whichcan have multiple such predefined portions to use for communicating databetween mobile stations and base stations.

The feedback information that can be provided from the mobile station tothe base station includes feedback information to recommend modulationand coding to be applied by the base station on downlink signaling(traffic data and/or control signaling and/or reference signaling)transmitted by the base station to the mobile station. In this case, thefeedback information includes an index (or other type of indicator) toenable selection of modulation and coding to be applied to signaling onthe downlink. In some examples, this index includes a precoding matrixindex (PMI) that can be used to apply precoding at the base station.

Another example of feedback information that can be sent from a mobilestation to a base station includes a channel quality indicator (CQI),which is an indication of wireless channel quality.

In accordance with some embodiments, the type of feedback informationthat is reported from the mobile station back to the base stationdepends on whether a predefined condition is satisfied. In someimplementations, this predefined condition is an indication of whetheror not the mobile station is a slow moving (or stationary) mobilestation or a fast moving (high velocity) mobile station. For a slowmoving mobile station, it is likely that parameters of the feedbackinformation do not change over several reporting periods, such thatreporting the same parameters in corresponding reporting periods isredundant. For a slow moving mobile station, instead of repeatedlysending the same parameters in successive reporting periods, differentfeedback information can be sent in the different reporting periods. Inother words, the reporting periodicity of different types of feedbackinformation for different users can be set to different values.

In some reporting modes, the feedback information (including CQI and/orPMI) that is sent from the mobile station to the base station is anaggregate feedback information that reflects the properties of multiplesubbands. The aggregate feedback information can be information thatreflects an average or some other aggregate of properties of multiplesubbands.

However, in accordance with some preferred embodiments, when thepredefined condition is detected, instead of sending aggregate feedbackinformation, individual feedback information for individual subbands canbe reported (referred to as “incremental feedback reporting”). Thus, forexample, instead of reporting an aggregate CQI for multiple subbands, anindividual CQI for an individual subband can be reported. Similarly,instead of reporting an aggregate PMI that is based on aggregateproperties of multiple subbands, an individual PMI can be reported foran individual subband.

From among a collection of subbands of a wireless channel, a subset ofthe subbands can be identified as being the preferred or “best” subbandsof the wireless channel. For example, M (M>1) subbands can beidentified. These M subbands can be used for communicating traffic dataor higher-layer signaling information between a base station and amobile station.

FIG. 1 shows an exemplary wireless network in which some embodiments ofthe invention can be provided. The wireless network includes a basestation 100 that includes an antenna array or other assembly (multi-beamantenna) 102 for sending wireless signals along multiple paths 104, 106(spatial beams) in a corresponding cell sector 108. In a differentimplementation, the antenna array 102 can include just a single antennafor sending wireless signals along one path.

A cell sector is one section of a cell of a cellular network. Althoughjust two paths 104 and 106 are depicted in FIG. 1, it is noted that morethan two paths (or just one path) can be provided in a cell sector inother embodiments. In alternative implementations, rather than providingmultiple beams in a cell sector, it is noted that multiple beams can beprovided in a cell. As used here, the term “cell segment” can refer toeither a cell sector or a cell.

Although just one base station is depicted in FIG. 1, it is noted that awireless network would typically include multiple base stations. In someembodiments, the wireless network is an LTE wireless network. Inalternative embodiments, other types of wireless networks can beemployed. Note that reference to “LTE wireless network” refers to awireless network that conforms to the requirements of the LTE standarddeveloped by 3GPP, as that standard is modified or evolved over time, aswell as to subsequent standards that evolve from LTE. Moreover, eventhough reference is made to LTE wireless networks in the ensuingdiscussion, it is noted that techniques according to preferredembodiments can also be applied to non-LTE, OFDM-based wirelessnetworks.

In an LTE wireless network, the base station 100 includes an enhancednode B (“eNode B”), which includes a base transceiver station thatincludes the antenna array 102. The base station 100 may also includes aradio network controller that cooperates with the enhanced node B. Theradio network controller and/or enhanced node B can perform one or moreof the following tasks: radio resource management, mobility managementfor managing mobility of mobile stations, routing of traffic, and soforth. Note that one radio network controller can access multiple eNodeBs, or alternatively, an eNode B can be accessed by more than one radioaccess controller.

More generally, the term “base station” can refer to a cellular networkbase station, an access point used in any type of wireless network, orany type of wireless transmitter to communicate with mobile stations.

As depicted in FIG. 1, the base station 100 includes one or more centralprocessing units (CPUs) 122, which is (are) connected to storage 124.Moreover, the base station 100 includes software 126 that is executableon the CPU(s) 122 to perform tasks of the base station 100, includingtasks according to preferred embodiments to enable support for SDMA inthe LTE wireless network.

The mobile station 110 of FIG. 1 also includes one or more CPUs 130 thatare connected to storage 132. The mobile station 110 also includessoftware 134 that is executable on the CPU(s) 130 to perform tasks ofthe mobile station 110.

The base station 100 is connected to a serving and/or packet datanetwork (PDN) gateway 112, which terminates the user plane interfacetoward the enhanced node B and assumes the responsibility for packetrouting and transfer towards an external network 114, which can be apacket data network such as the Internet or other type of network.

The arrangement depicted in FIG. 1 is provided for purposes of example.In other implementations, other wireless network arrangements are used.

As noted above, in accordance with some embodiments, incrementalreporting of feedback information including CQI and PMI can beperformed. In one implementation, the reporting of such feedbackinformation can be in the physical uplink shared channel (PUSCH).However, in other implementations, feedback information can be providedin other types of channels or messages sent from the mobile station tothe base station, e.g., the physical uplink control channel (PUCCH).Generally, feedback information is referred to as being sent in areport, where a “report” can include a message, fields of a message,multiple messages, and so forth.

According to some implementations, two modes of operation as defined bythe LTE standards can employ the incremental feedback reportingaccording to preferred embodiments. These two modes of operation includeLTE PUSCH reporting Mode 2-0 and Mode 2-2. PUSCH reporting Mode 2-0 asdefined by LTE is used for single input, multiple output (SIMO)communication, spatial frequency block coding (SFBC) communication, oropen-loop spatial multiplexing (SM) communication. In this reportingmode, the precoding information is not included in the feedback.

Mode 2-2 according to LTE refers to closed loop MIMO (multiple input,multiple output) communication, where closed-loop MIMO uses feedbackinformation to apply coding. For example, based on feedback information(in the form of a PMI) from the mobile station, the base station appliesa selected precoding.

Although reference is made to LTE Mode 2-0 and Mode 2-2 in thisdiscussion, it is noted that incremental feedback reporting according topreferred embodiments can also be applied to other types of wirelesscommunications.

Incremental reporting of individual CQIs is depicted in FIG. 2 for anenhanced LTE PUSCH reporting Mode 2-0. Four reports are depicted in FIG.2 for four successive reporting time intervals (1, 2, 3, 4). In oneimplementation, these four reports are carried by PUSCH from the mobilestation to the base station. The report that is sent from the mobilestation to the base station includes a bitmap field 202 that contains abitmap, a subband CQI information field 204 that selectively contains anaggregate CQI or individual CQI, and a wideband CQI information field206 that contains a wideband CQI. The bitmap identifies the M preferredsubbands. The bitmap includes a number of bits that correspond torespective subbands. Setting a respective one of the bits means that acorresponding subband is identified as preferred. In otherimplementations, other types of data structures can be used to indicatewhich subbands are preferred.

The subband CQI information field 204 can either include an aggregateCQI for the M subbands identified by the bitmap, or an individual CQIfor one of the M subbands. In reporting time interval 1, as shown inFIG. 2, the subband CQI information field 204 contains an aggregate CQIover the M subbands. The wideband CQI information field 206 contains theaggregate CQI over the entire wireless channel including all thesubbands.

It is assumed that in reporting interval 1, the predefined conditiondiscussed above is not satisfied, such that the CQI that is communicatedin the subband CQI information field 204 is an aggregate CQI over the Msubbands. In some embodiments, the predefined condition is based on thecontent of the bitmap. If the current bitmap is the same as a priorbitmap (in a prior reporting interval), then the predefined condition issatisfied. However, if the current bitmap is different from a priorbitmap in a prior reporting interval, then the predefined condition isnot satisfied. The bitmap staying the same in successive reportingintervals is an indication that the mobile station is a slow moving orstationary mobile station.

In the example of FIG. 2, it is assumed that in each of the reportingintervals 2-4, the bitmap remains the same as the bitmap reported intime interval 1. In reporting interval 2, the subband CQI informationfield 204 includes the individual CQI for a first individual subbandfrom among the M subbands. Similarly, in reporting intervals 3 and 4,the subband CQI information fields 204 of the respective reports containindividual CQIs for corresponding second and third subbands from the Msubbands. Thus, when the bitmap does not change, individual CQIs can bereported rather than the aggregate CQI.

Although FIG. 2 shows an implementation in which just one individual CQIfor a corresponding individual subband can be included in each report,it is noted that in alternative implementations multiple individual CQIsfor corresponding subbands can be included in one report.

FIG. 3 shows reports sent in four different reporting intervals (1, 2,3, 4) for on enhanced LTE PUSCH reporting Mode 2-2. Mode 2-2, inaddition to CQI information, PMI information is also provided (sinceclosed loop MIMO is used). Moreover, in Mode 2-2, it is assumed thatthere are two transmitting codewords such that CQI information for thetwo transmitting codewords are reported separately. In each report shownin FIG. 3, a bitmap field 302 contains the bitmap, a first subband CQIfield 304 contains the subband CQI information for a first transmittingcodeword, a wideband CQI field 306 contains the wideband CQI, a secondsubband CQI information field 308 contains the subband CQI informationfor a second transmitting codeword, and a PMI information field 310contains PMI information. In the reporting interval 1 of FIG. 3, it isassumed that the current bitmap is different from the prior bitmap (inthe prior reporting interval). As a result, the subband CQIs provided inthe subband CQI information fields 304 and 308, as well as the PMIinformation in the PMI information field 310, are aggregate CQIs andPMI, respectively, for the M subbands identified by the bitmap in thefield 302.

However, in reporting intervals 2-4, it is assumed that the bitmap staysthe same as the bitmap in reporting interval 1, in which case thesubband CQI information fields 304 and 308 can include individual CQIsfor corresponding transmitting codewords, with different individual CQIsfor different subbands reported in successive reporting intervals.

Also, in reporting time intervals 2-4, the PMI information contained inthe PMI information field 310 includes the individual PMI for anindividual subband, with different individual PMIs reported forcorresponding subbands in successive reporting time intervals 2-4.

FIGS. 4 and 5 depict operations of a mobile station and base station,respectively, for an enhanced PUSCH reporting Mode 2-0 operation. In acurrent reporting interval, the mobile station determines (at 402) ifthe present bitmap is the same as the prior bitmap. If not, the CQIinformation reported (at 404) in the subband CQI information field 204(FIG. 2) is the aggregate CQI over the M subbands. However, if thecurrent bitmap is the same as the prior bitmap, then the CQI informationreported (at 406) in the subband CQI information field 204 is theindividual CQI for corresponding individual subband.

As shown in FIG. 5, the base station determines (at 502) if the presentbitmap is the same as the prior bitmap. If not, then the base stationuses (at 504) the aggregate CQI that was previously received. However,if the current bitmap is the same as the prior bitmap, then the basestation uses (at 506) the individual CQI for a selected subband that isused for transmission of downlink data from the base station to themobile station.

FIGS. 6 and 7 depict the enhanced PUSCH reporting Mode 2-2 operation ofthe mobile station and base station, respectively. In FIG. 6, the mobilestation determines (at 602) if the present bitmap is the same as theprior bitmap. If not, then the subband CQI information fields 304 and308 and the PMI information field 310 (FIG. 3) of the feedback reportare provided (at 604) with aggregate CQI and PMI information for the Msubbands. However, if the current bitmap is the same as the priorbitmap, then individual CQIs and an individual PMI are provided (at 606)in corresponding fields 304, 308, and 310 as depicted in time interval2, 3, or 4 of FIG. 3.

FIG. 7 illustrates the operation of the base station. The base stationdetermines (at 702) if the current bitmap is the same as the priorbitmap. If not, the base station uses (at 704) the aggregate CQIs andaggregate PMI for transmitting downlink information to the mobilestation. On the other hand, if the current bitmap is the same as theprior bitmap, then the base station uses (at 706) the correspondingindividual CQIs and individual PMI for the selected subband that is usedby the base station for communicating data to the mobile station.

In the foregoing discussion, it is assumed that the mobile station makesthe decision regarding whether incremental reporting of individual CQIsand/or PMIs for subbands is to be performed. In an alternativeembodiment, it is the base station that makes the decision regardingwhether or not the mobile station should send individual feedbackinformation for individual subbands.

For example, as shown in FIG. 8, the base station can decide that thebase station wishes to receive individual feedback information aboutindividual subbands from the mobile station. In response to making sucha decision, the base station sends (at 802) a control indication to themobile station. The control indication can be in the form of a higherlayer control signaling, such as Radio Resource Control (RRC) signaling,for example. The control indication can be sent in response to the basestation determining that a predefined condition is satisfied, such asthe bitmap not changing in successive reporting intervals.

In response to the control indication, the mobile station sends (at 804)individual feedback information (individual CQI(s) and/or individualPMI(s)) for individual subband(s) to the base station. The individualfeedback information can be communicated in a physical uplink controlchannel (PUCCH) or other channel.

However, if the base station determines that the predefined condition isnot satisfied, then the base station sends another control indication tocause the mobile station to send aggregate feedback information forplural subbands.

The tasks of FIGS. 4-8 can be performed by software in the mobilestation 110 or base station 100 of FIG. 1. Instructions of such softwareare executed on a processor (e.g., CPUs 130 and 122 in FIG. 1). Theprocessor includes microprocessors, microcontrollers, processor modulesor subsystems (including one or more microprocessors ormicrocontrollers), or other control or computing devices. A “processor”can refer to a single component or to plural components (e.g., one ormultiple CPUs).

Data and instructions (of the software) are stored in respective storagedevices, which are implemented as one or more computer-readable orcomputer-usable storage media. The storage media include different formsof memory including semiconductor memory devices such as dynamic orstatic random access memories (DRAMs or SRAMs), erasable andprogrammable read-only memories (EPROMs), electrically erasable andprogrammable read-only memories (EEPROMs) and flash memories; magneticdisks such as fixed, floppy and removable disks; other magnetic mediaincluding tape; and optical media such as compact disks (CDs) or digitalvideo disks (DVDs).

In the foregoing description, numerous details are set forth to providean understanding of the present invention. However, it will beunderstood by those skilled in the art that the present invention may bepracticed without these details. While the invention has been disclosedwith respect to a limited number of embodiments, those skilled in theart will appreciate numerous modifications and variations therefrom. Itis intended that the appended claims cover such modifications andvariations as fall within the true spirit and scope of the invention.

What is claimed is:
 1. A method of reporting feedback informationregarding a wireless channel comprising: determining whether a parameterof aggregate feedback information regarding plural subbands included ina prior report sent to a base station has not changed; in response todetermining that the parameter has not changed, including, in a firstreport to be sent to a base station, feedback information regarding anindividual one of plural subbands of the wireless channel; and inresponse to determining that the parameter has changed, including, in asecond report to be sent to the base station, aggregate feedbackinformation regarding the plural subbands.
 2. The method of claim 1,wherein the parameter of aggregate feedback information is a datastructure identifying preferred subbands.
 3. The method of claim 2,wherein determining if the data structure identifying preferred subbandshas not changed comprises determining if a bitmap identifying thepreferred subbands has not changed.
 4. The method of claim 1, furthercomprising: after sending the first report, including, in a third reportto be sent to the base station, further feedback information regarding asecond individual one of the plural subbands if the parameter has notchanged.
 5. The method of claim 1, further comprising: including in thefirst report further feedback information regarding a second individualone of the plural subbands.
 6. The method of claim 1, furthercomprising: performing data communication using one or more of theplural subbands that are less than all available subbands of thewireless channel.
 7. The method of claim 1, wherein the feedbackinformation is for a closed loop MIMO (multiple input, multiple output)mode of operation.
 8. The method of claim 7, wherein the mobile stationis to transmit plural codewords, and wherein the feedback informationincluded in the first report is for a first of the plural codewords, andwherein the first report further includes feedback information for anindividual subband for another one of the plural codewords.
 9. Themethod of claim 1, wherein the feedback information in the first reportfor the individual subband comprises at least one of: a precoding matrixindex (PMI); and channel quality indicator (CQI).
 10. A base stationcomprising: an interface to communicate wirelessly over a wirelesschannel with a mobile station; and a processor configured to: determinewhether a parameter of aggregate feedback information regarding pluralsubbands for a current reporting interval has not changed from aparameter of aggregate feedback information regarding plural subbandsfor a prior reporting interval; in response to determining that theparameter has not changed, using individual feedback information for anindividual subband of plural subbands of the wireless channel; and inresponse to determining that the parameter has changed, using aggregatefeedback information for the plural subbands.
 11. The base station ofclaim 10, wherein the individual feedback information or aggregatefeedback information is used for downlink signaling and traffic data tobe sent to the mobile station.
 12. The base station of claim 10, whereinthe individual feedback information comprises at least one of: anindividual channel quality indicator (CQI); and an individual precodingmatrix index (PMI).
 13. The base station of claim 10, wherein todetermine whether the parameter has not changed the processor is furtherconfigured to: determine if a bitmap for a current reporting interval isunchanged from a bitmap for a prior reporting interval, wherein thebitmap identifies the plural subbands.
 14. A mobile station comprising:an interface to communicate wirelessly over a wireless channel with abase station; and a processor configured to: determine whether aparameter of aggregate feedback information regarding plural subbandsincluded in a prior report sent to a base station has not changed; inresponse to determining that the parameter has not changed, include, ina first report to be sent to a base station, individual feedbackinformation regarding an individual one of plural subbands of thewireless channel; and in response to determining that the parameter haschanged, including, in a second report to be sent to the base station,aggregate feedback information regarding the plural subbands.
 15. Themobile station of claim 14, wherein the first report includes a bitmapidentifying the plural subbands as being preferred subbands.
 16. Themobile station of claim 14, wherein the individual feedback informationincludes at least one of: an individual channel quality indicator (CQI);and an individual precoding matrix index (PMI).
 17. The mobile stationof claim 14, wherein to determine whether the parameter has not changedthe processor is further configured to: determine whether a bitmapidentifying the plural subbands remains the same in successive reportingintervals.
 18. The mobile station of claim 14, wherein the feedbackinformation is for a closed loop MIMO (multiple input, multiple output)mode of operation.
 19. The mobile station of claim 18, wherein themobile station is to transmit plural codewords, and wherein the feedbackinformation included in the first report is for a first of the pluralcodewords, and wherein the first report further includes feedbackinformation for an individual subband for another one of the pluralcodewords.
 20. The mobile station of claim 14, wherein the processor isfurther configured to: after sending the first report, including, in athird report to be sent to the base station, further feedbackinformation regarding a second individual one of the plural subbands ifthe parameter has not changed.